1. Field of the Invention
The present invention relates to a process for the separation of metallurgical products such as, for example, ingots, slabs or plate-shaped workpieces, and in particular for the transverse division of the cast strand in continuous casting plants and for the longitudinal division of continuous cast ingots which have previously been cut into lengths, in which the products are divided using one or several oxyacetylene or plasma cutting torches disposed on one side of the products and by following a prescribed cutting line and in which a front cutting edge is formed on the surface of the products facing the cutting torches and a rear cutting edge is formed on the other side of the products. The invention further relates to an apparatus for carrying out the process.
2. Description of the Prior Art
The foregoing type processes are used, among other places, in cases where ingots, billets or slabs, or also metallic plate-shaped workpieces of lesser thickness, are to be cut to predetermined lengths and/or widths. Thus, such processes are used, for example, in the transverse division of a strand divided while still hot into single continuous cast ingots directly after the last pinch rolls of the casting plant have been passed. In practice, such processes are also used to longitudinally divide hot cast ingots which have previously been cut into lengths directly and without delay, or to divide such ingots longitudinally only after the ingots have been discharged and have cooled.
In such processes, separation is usually carried out using at least one oxyacetylene cutting torch. It is also known to use two oxyacetylene cutting torches for each cutting point in order to increase cutting speed. Attempts have also recently been made to use plasma cutting torches in such processes. The purpose of such processes is to obtain a satisfactory quality in the surface and edges of the cutting joints, and in particular to produce surfaces and edges which do not need any finishing.
In a process of this type described in German Offenlegungsschrift No. 27 18 748, separation is carried out using a cutting torch which is disposed above the product being cut and is supported on a carrier bracket. The product is preferably disposed horizontally on a base and the axis of the cutting torch is disposed so that the cutting jet is directed downwardly from the cutting torch. At the beginning of the cutting process, the cutting torch is moved with the aid of the carrier bracket to the edge of the product from which cutting is to start. When preheating has been achieved, the operation is switched over to cutting. At the same time, the forward movement of the movable carrier bracket, or in the case of transverse division in continuous casting plants, the forward movement of the movable torch, is switched to the carrier bracket which is fixed in relation to the product, and the torch follows a predetermined cutting line towards the opposite edge of the product. The time necessary to achieve separation can be reduced by using two individual cutting torches which move towards one another from opposing edges of the product. To reduce cutting time, it has also been suggested to use two oxyacetylene cutting torches disposed one behind the other in the cutting direction which are adjustable independently of one another and form a common cutting joint in the product to carry out the cutting. In either case, i.e., where only one cutting torch is used or two cutting torches are used, a cutting surface is formed at the cutting point.
The term "cutting surface" as used herein means the reaction surface of the cutting process on which the cutting jet of the cutting torch or torches melts and removes the material during the cutting process. The cutting surface has, as viewed in the flow direction of the cutting jet or jets, a front cutting edge on the surface of the product facing the cutting torch or torches and a rear cutting edge on the opposite side of the product, the cutting edges being located above and below, respectively, in the case of horizontal products lying on a base. The rear or lower cutting edge thereby passes at its two ends into one of the two rear or lower edges of the finished cutting joint.
Known torch cutting processes using either one or two cutting torches per cutting point have the disadvantage that thick beads of a solidified metal-slag mixture, so-called "flame burrs", are formed at the edges of the cutting joint on the underside of the product. These "flame burrs" are composed of a portion of the metal of the cutting joint which is melted by the cutting torches, partially burnt and pulled downwardly by the cutting jet of the cutting torch or torches. A certain amount of the metal-slag mixture falls off the ingot in droplets, while the other part solidifies on the edges of the finished cutting joint, sometimes forming beads several centimeters thick. Practice has now shown that billets and ingots with such "flame burrs" can not be hot rolled in this condition directly following the separation process and it is necessary to remove the "flame burrs" beforehand, e.g., by grinding, planing or by flame descaling. In many cases an expensive turn-over device is necessry in addition to this removal operation.
In order to eliminate these disadvantages, German Offenlegungsschrift No. 27 18 748 teaches that the torch should be moved beneath the product with the cutting jet directed upwardly. According to this publication, no "flame burrs" are formed in such a process and the material ejected out of the cutting joint which drops onto the surface of the product supposedly does not affect subsequent rolling of the product and does not need to be removed. However, in actual fact, deposits are also formed on the upper edges of the cutting joint in this process and the surfaces obtained on the cutting joint are not clean and even. A further disadvantage of this process is that undesirable contamination is caused by the large amount of smoke formed and the ejected material sprayed over a wide area around the cutting point. Such contamination must be prevented by using specially-designed apparatus.
German Pat. No. 12 12 393 describes a process in which a pressurized water jet is directed obliquely from beneath the product onto the slag issuing from the cutting joint during torch cutting in vertical continuous casting plants in order to prevent a slag "burr" from forming. This method, however, has proven to be impractical since it requires a high water consumption and an additional water cleaning unit.